1. Field of the Invention
The present invention relates to semiconductor memory devices, and particularly to semiconductor memory devices including address transition detecting circuits, and an operating method thereof.
2. Description of the Background Art
FIG. 7 is a block diagram showing one example of a conventional dynamic random access memory (hereinafter referred to as DRAM). In FIG. 7, a memory array 1 includes a plurality of dynamic type memory cells arranged in a matrix, and a decoder selecting any one of the plurality of dynamic type memory cells. An address buffer 2 receives externally applied address signals A0-An to generate internal address signals a0-an. The decoder in the memory array 1 decodes the internal address signals a0-an to select a memory cell of an address designated by the internal address signals a0-an.
A RAS buffer 3 receives an external row address strobe signal /RAS to generate an internal row address strobe signal .phi..sub./RAS. A CAS buffer 4 receives an external column address strobe signal /CAS to generate an internal column address strobe signal .phi..sub./CAS.
The internal row address strobe signal .phi..sub./RAS is an internal signal for activating the entire system, and changes in synchronization with the external row address strobe signal /RAS. The internal column address strobe signal .phi..sub./CAS is an internal signal for activating a column system, and changes in synchronization with the external column address strobe signal /CAS.
A write control circuit 5 generates write control signals .phi..sub.WR, .phi..sub.WDE, and .phi..sub.WT in response to an external write enable signal /WE, the internal row address strobe signal .phi..sub./RAS and the internal column address strobe signal .phi..sub./CAS. An input buffer circuit 6 provides data D applied to an input/output terminal IOT to a data bus line DB in response to the write control signal .phi..sub.WR. A write buffer circuit 7 provides the data on the data bus line DB to an input/output bus line IOB in response to the write control signal .phi..sub.WDE.
An ATD generating circuit 8 responds to the internal row address strobe signal .phi..sub./RAS, the write control signal .phi..sub.WT and a control signal .phi..sub.a to detect transitions of the internal address signals a0-an to generate an ATD (address transition detection) signal .phi..sub.ATD. An output control circuit 9 generates output control signals .phi..sub.PA, and .phi..sub.DOT in response to the ATD signal .phi..sub.ATD.
A preamplifier circuit 10 responds to the output control signal .phi..sub.PA to amplify the data on the input/output bus line IOB and provides the amplified data to the data bus line DB. A main amplifier circuit 11 responds to the output control signal .phi..sub.DOT to amplify and hold the data on the data bus line DB, and applies the held data to the input/output terminal IOT in response to an external output enable signal OE.
Reading and writing operations of the DRAM will now be described.
In a reading cycle, when the internal address signals a0-an change, the ATD generating circuit 8 generates the ATD signal .phi..sub.ATD, while in the memory array 1, the data is read from an address designated by the internal address signals a0-an to the input/output bus line IOB. The output control circuit 9 first generates the output control signal .phi..sub.PA in response to the ATD signal .phi..sub.ATD. The preamplifier circuit 10 responds to the output control signal .phi..sub.PA to amplify the data read to the input/output bus line IOB, and applies the amplified data to the data bus line DB.
The output control circuit 9 then generates the output control signal .phi..sub.DOT. The main amplifier circuit 11 responds to the output control signal .phi..sub.DOT to amplify and hold the data on the data bus line DB. In addition, the main amplifier circuit 11 responds to the external output enable signal OE to output the held data to the input/output terminal IOT.
In a writing cycle, the write control circuit 5 first generates the write control signal .phi..sub.WR. The input buffer circuit 6 responds to the write control signal .phi..sub.WR to input and amplify the data D externally applied to the input/output terminal IOT, and applies the amplified data to the data bus line DB.
The write control circuit 5 then generates the write control signal .phi..sub.WDE. The write buffer circuit 7 responds to the write control signal .phi..sub.WDE to input and amplify the data on the data bus line DB, and applies the amplified data to the input/output bus line IOB. The data on the input/output bus line IOB is written in an address in the memory array 1 designated by the internal address signals a0-an.
At the end of the writing operation, the write control circuit 5 generates the write control signal .phi..sub.WT. The ATD generating circuit 8 is activated in response to the write control signal .phi..sub.WT, to generate the ATD signal .phi..sub.ATD, so that in the same manner as that of the reading cycle, the data written in the memory array 1 is provided to the data bus line DB through the input/output bus line IOB and the preamplifier circuit 10, and further amplified and held by the main amplifier circuit 11.
FIG. 8 shows a signal waveform diagram of a writing cycle. As can be seen from FIG. 8, the write control signal .phi..sub.WR first rises, and thereafter the write control signal .phi..sub.WDE rises. Consequently, the data externally applied to the input/output terminal IOT is written in the memory array 1 through the input buffer 6 and the write buffer 7.
At the end of the writing operation, the write control signal .phi..sub.WT rises. In response to the rise of the write control signal .phi..sub.WT, the ATD signal .phi..sub.ATD rises. The output control signal .phi..sub.PA and the output control signal .phi..sub.DOT then rise sequentially. Consequently, the data written in the memory array 1 is provided through the preamplifier circuit 10 to the main amplifier circuit 11 and held therein.
The reason for reading the data written in the memory array 1 to the main amplifier circuit 11 at the end of the writing operation will be described in the following.
As described above, reading operation is carried out in response to the ATD signal .phi..sub.ATD. However, in the case of writing data to a certain address in the memory cell array 1 and reading the data from the same address thereafter, the ATD signal .phi..sub.ATD is not generated since the internal address signals a0-an do not change. Therefore, the preamplifier circuit 10 and the main amplifier circuit 11 do not operate, and the data read from the memory array 1 can not be output.
In order to avoid this, the ATD generating circuit 8 is activated by the write control signal .phi..sub.WT at the end of the writing operation, so that the data written in the memory array 1 can be held in the main amplifier circuit 11.
FIG. 9 is a schematic diagram showing a detailed structure of the write control circuit 5. The write control circuit 5 includes signal generating circuits 51, 52, 53, and 54. The signal generating circuit 51 includes a NOR gate G1, inverters G2, G3, and G4 and NAND gates G5, G6, and G7. The signal generating circuit 52 includes inverters G8, G9, G10, and G12 and a NAND gate G11. The signal generating circuit 53 includes inverters G13, G14, and G15 and a NOR gate G16. The signal generating circuit 54 includes inverters G17, G18, and G19 and a NOR gate G20.
The signal generating circuit 51 generates a control signal .phi..sub.W in response to the external write enable signal /WE, the internal row address strobe signal .phi..sub./RAS and the internal column address strobe signal .phi..sub./CAS. The signal generating circuit 52 generates the write control signal .phi..sub.WR in response to the control signal .phi..sub.W. The signal generating circuit 53 generates the write control signal .phi..sub.WDE in response to the write control signal .phi..sub.WR. The signal generating circuit 54 generates the write control signal .phi..sub.WT in response to the control signal .phi..sub.W.
As can be seen in FIG. 8, when the internal column address strobe signal .phi..sub./CAS falls to "L", with the external write enable signal /WE and the internal row address strobe signal .phi..sub./RAS being both in an "L" state, the control signal .phi..sub.W attains "H" (writing state). When the internal column address strobe signal .phi..sub./CAS rises to "H" thereafter, the control signal .phi..sub.W falls to "L".
In response to the rise of the control signal .phi..sub.W, the write control signal .phi..sub.WR rises to "H", and falls to "L" after a prescribed time. In response to the fall of the write control signal .phi..sub.WR, the write control signal .phi..sub.WDE rises to "H", and falls to "L" after a prescribed time. In response to the fall of the control signal .phi..sub.W, the write control signal .phi..sub.WT rises to "H", and falls to "L" after a prescribed time.
FIG. 10 is a schematic diagram showing a detailed structure of the input buffer circuit 6. The input buffer circuit 6 includes a NOR gate G21, inverters G22, G23, G24, G25, G26, and G27, P channel MOS transistors P1, P2, P3, and P4 and N channel MOS transistors N1, N2, N3, and N4. The transistors P1, P2, N1, and N2 constitute an inverter 61, and the transistors P3, P4, N3, and N4 constitute an inverter 62. The inverters G24 and G25 constitute a latch circuit L1.
When the internal row address strobe signal .phi..sub./RAS is "L", the data D externally applied to the input/output terminal IOT is applied through the NOR gate G21 and the inverter G22 to the inverter 61.
When the write control signal .phi..sub.WR becomes "H", the inverter 61 is activated, whereby the data is input and latched in the latch circuit L1. When the control signal .phi..sub.W is "H", the inverter 62 is in an activated state, whereby the data latched in the latch circuit L1 is applied through the inverters G26, 62 to the data bus line DB.
FIG. 11 is a schematic diagram showing a detailed structure of the write buffer circuit 7. The write buffer circuit 7 includes N channel MOS transistors N5, N6, N7, and N8, NOR gates G30 and G31, and inverters G28 and G29. The input/output bus line IOB includes a pair of input/output lines IO1 and I02.
When the write control signal .phi.WDE attains "H", the data on the data bus line DB is applied through the inverter G28 and the NOR gate G30 to the gates of the transistors N5 and N8, and through the NOR gate G31 to the gates of the transistors N6 and N7, so that the data on the data bus line DB is applied to the input/output line IO1, and the inverted data of the data on the data bus DB is applied to the input/output line I02. That is, the input/output lines IO1, and I02 are supplied with complementary data.
FIG. 12 is a schematic diagram showing a detailed structure of the ATD generating circuit 8. The ATD generating circuit 8 includes a NOR gate G32, an inverter G33, N channel MOS transistors N9, N10, and N11, and detecting circuits 81-8n.
The detecting circuits 81-8n respectively detect transitions of the internal address signals a0-an to generate detection pulses .phi..sub.c0 -.phi..sub.cn. The NOR gate G32 generates an output signal "H", when the internal row address strobe signal .phi..sub./RAS and the control signal .phi..sub.a attain "L".
As is shown in FIG. 13, when any of the detecting circuits 81-8n generates the detection pulse .phi..sub.ci (i=0-n), either of the transistors N9-N10 is turned on, whereby a pulse appears on the ATD signal .phi..sub.ATD provided from the inverter G33. When a pulse is generated on the write control signal .phi..sub.WT, the transistor N11 is turned on, and a pulse appears on the ATD signal .phi..sub.ATD. The control signal .phi..sub.a is a delay signal of the internal row address strobe signal .phi..sub./RAS.
FIG. 14 is a schematic diagram showing a detailed structure of the output control circuit 9. The output control circuit 9 includes signal generating circuits 91, 92. The signal generating circuit 91 includes inverters G34, G35, and G36 and a NOR gate G37. The signal generating circuit 92 includes inverters G38, G39, and G40 and a NOR gate G41.
The signal generating circuit 91 responds to the ATD signal .phi..sub.ATD to generate the output control signal .phi..sub.PA. The signal generating circuit 92 responds to the output control signal .phi..sub.PA to generate the output control signal .phi..sub.DOT.
As can be seen in FIG. 13, the output control signal .phi..sub.PA rises to "H" in response to a fall of the ATD signal .phi..sub.ATD, and after a prescribed time period falls to "L". The output control signal .phi..sub.DOT rises to "H" in response to a fall of the output control signal .phi..sub.PA, and after a prescribed time period falls to "L".
FIG. 15 is a schematic diagram showing a detailed structure of the preamplifier circuit 10. The preamplifier circuit 10 includes P channel MOS transistors P5-P9, N channel MOS transistors N12-N17, and inverters G42-G45. The transistors P5, P6, N12, N13, and N14 constitute an amplifier 101. The transistors P7 and N15 constitute a transfer gate 102. The inverters G43 and G44 constitute a latch circuit 103. The transistors P8, P9, N16, and N17 constitute an inverter 104.
When the output control signal .phi..sub.PA is "H", the amplifier 101 is activated, so that the data on the input/output lines IO1, and I02 is amplified by the amplifier 101 to be applied to the transfer gate 102. When the output control signal .phi..sub.PA is "H", the transfer gate 102 is turned on, so that the data amplified by the amplifier 101 is applied to the latch circuit 103 and latched therein. The inverter 104 is activated when the control signal .phi..sub.W is "L", so that the data latched in the latch circuit 103 is applied to the data bus line DB.
FIG. 16 is a schematic diagram showing a detailed structure of the main section of the main amplifier circuit 11. The main amplifier circuit 11 includes a clocked inverter G46, inverters G47, G48, and G49, NAND gates G50 and G51, and N channel MOS transistors N18, and N19. The inverter G47 and G48 constitute a latch circuit 111.
When the output control signal .phi..sub.DOT is "H", the clocked inverter G46 is activated, whereby the data on the data bus line DB is applied to the latch circuit 111 and held therein. When the external output enable signal OE is "H", the data latched in the latch circuit 111 and the inverted data thereof are respectively applied through the NAND gate G50 and G51 to the gates of the transistors N18 and N19, and consequently the data is applied to the input/output terminal IOT.
As described above, a conventional DRAM needs to activate the ATD generating circuit 8 and the preamplifier circuit 10 at the end of the writing operation. A problem of increase of a consumed current thus arises.